1. Field of the Invention
This invention relates to the art of power supply voltage regulation, and particularly to conversion systems for providing constant current or voltage from an AC source which varies widely in magnitude and/or frequency.
2. Description of the Prior Art
It is known in the prior art to supply DC voltage and current to a load when only AC is available. It is also known to regulate the output of such supplies so that a variation in AC input magnitude will leave the output substantially unaltered.
The prior art, however, in the design of such power supplies generally achieves output regulation by use of various electronic input power dissipating devices such as vacuum tubes solid state devices, resistors and transformers. A typical approach samples the output magnitude and controls conductivity of variable impedance devices in response thereto, thus achieving stabilization. Feedback is used to control the gain of amplifiers, for example, whether AC or DC, and thus to regulate the output. Other devices employ various constant voltage or constant current devices across the output or in a feedback path to maintain regulation. Representative patents in the prior art include U.S. Pat. Nos. 3,697,854; 3,676,768; 3,219,906; 3,569,816; 3,219,907; 3,806,792 and 3,818,308.
Such prior art approaches often have a limitation on the allowable input voltage variation, to the order of .+-. 10-20%. In many instances, the design of the prior art circuit is dependent on the operating frequency and voltages of the input voltage source, so that at most, only minimal variations therein may be tolerated. For example, most supplies designed to function properly in a U.S.A. environment of 110 VAC at 60Hz will not function on a European current of 220 VAC at 50Hz.
In particular, when transformer means are employed for isolation purposes, the transformer is often designed to handle the unregulated input currents from the largest voltages which the input source may attain without saturation. In cases where wide variations of input voltage occur, e.g., 5:1 ratios, the transformer's large designed core size is largely wasted when the lower voltages are utilized. The same trade-offs of size and expense can occur when other inductive means are employed over a wide range of input voltages or frequencies. Thus, in forcing the design of inductive means to be dictated by the upper regions of voltages utilized to handle a maximum flux, large inefficiencies necessarily result during low voltage operations.
It thus becomes apparent that the prior art power supplies may be used in limited environments.